The present invention concerns hydrocarbon soluble borated derivatives of oxazolines, their method of preparation, and the utility of said borated oxazolines as lubricating oil additives, which markedly improve the sludge dispersancy-varnish inhibiting properties of lubricating oils employed for crankcase lubrication of internal combustion engines.
There are two principal environments which are encountered by automotive crankcase lubricants, i.e. cyclical high and low temperatures from stop-and-go driving and continuous high temperatures from extended operation of the automobile over long distances. Each of these environments provokes the presence in the lubricant of varying proportions of foreign particles such as dirt, soot, water and decomposition products resulting from breakdown of the oil. This foreign matter appears responsible for the deposition of a mayonnaise-like sludge which circulates with the oil.
Besides sludge formation, the inner surfaces tend to develop a varnish deposit which results from the operation of the engine at continuous high temperatures. In such an environment, oil breakdown results in the formation of acidic materials which in themselves corrode the metal surfaces of the bearings, pistons, etc., as well as catalyze the decomposition of the lubricating oil which decomposition is manifested in hard, carbonaceous deposits which accumulate in the piston ring groove and form a varnish on the piston skirts and other metal surfaces.
During the past decade, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants in keeping the engine clean of deposits and permitting extended crankcase oil drain periods while avoiding the undesirable environmental impact of the earlier used metal-containing additives. Most commercial ashless dispersants fall into several general categories. In one category, an amine or polyamine is attached to a long-chain hydrocarbon polymer (the oil solubilizing portion of the molecule), usually polyisobutylene through an acid group, such as a monocarboxylic acid, for example, see U.S. Pat. No. 3,444,170 or a dicarboxylic acid material such as polyisobutenyl succinic anhydride, by forming amide or imide linkages such as described in U.S. Pat. Nos. 3,172,892 and 3,272,746 and may include the reaction product of such materials with boron (see U.S. Pat. Nos. 3,087,936 and 3,254,025) generally forming a mixed boric acid salt which is hydrolytically rather unstable reducing its usefulness.
Reaction products of acylated nitrogen intermediates (from the reaction of an alkenyl succinic acid producing compound and a hydroxy hydrocarbon amine) and a boron compound are taught as additives for lubricants in U.S. Pat. No. 3,282,955; however, they have not been commercially successfull probably because of inadequate sludge dispersant activity.
Reaction products of hydrocarbon substituted succinic anhydride, e.g., polyisobutenylsuccinic anhydride, with compounds containing both an amine group and a hydroxy group have been suggested or investigated in the prior art. For example, United Kingdom Specification No. 809,001 teaches corrosion inhibitors comprising a multiple salt complex derived from the reaction product of hydrocarbyl substituted dicarboxylic acids and hydroxy amines (including 2-amino-2-methyl-1,3-propanediol) [AMP] and tris-(hydroxymethyl)-amino methane [THAM]. Further, United Kingdom Specification No. 984,409 teaches ashless, amide/imide/ester type lubricant additives prepared by reacting an alkenylsuccinic anhydride, said alkenyl group having 30 to 700 carbon atoms, with a hydroxy amine including THAM. In contrast to the foregoing, German (DOS) No. 2,512,201 teaches that the reaction of a hydrocarbyl dicarboxylic acid material, i.e. acid or anhydride, or ester, with certain classes of amino alcohols, under certain conditions including metal salt promotion, will result in products containing one or two heterocyclic ring structures, namely, an oxazoline ring, and that products containing at least one oxazoline ring can be tailored for various functions, such as anti-rust agents, detergents, or dispersants for oleaginous compositions including lube oil, gasoline, turbine oils and oils for drilling applications. In none of the foregoing is there any suggestion that the reaction products could be usefully borated.
In contrast to the lubricating oil additive teachings of the prior art, mono-oxazolines have been usefully borated for gasoline additive applications to alleviate the adverse effects of combustion engine deposits, suppress surface ignition and carburetor icing (see U.S. Pat. Nos. 2,948,597; 2,965,459; 2,993,765; 3,030,374; 3,030,375; 3,070,603). Such gasoline additives are not suitable for lubricating oils since they lack satisfactory sludge dispersant activity and offer no teaching that they would be useful to inhibit the acid-induced catalytic decomposition of the lubricating oil.
Dicarboxylic acid lactone type products have also been provided with anti-rust and/or dispersant properties by reaction with hydroxy amines such as ethanolamine and diethanolamine (see U.S. Pat. Nos. 3,248,187 and 3,620,977).